The present invention relates to a device for electrical measurement of the level of a liquid contained in the fuel tank of a vehicle. The device has a dip tube sensor mountable on the tank and dippable into the liquid, this sensor having a dip tube with its end extending to the bottom of the tank and a float disposed therein and acting as a floatation body. The dip tube sensor has a first contact bridge with two wiper contacts, with at least one wiper contact being in conductive connection with a resistance strip and another wiper contact being in conductive connection with a contact strip. Both these strips extend along the length of the dip tube. A level indicating device is connected to the terminals of the resistance and contact strips. In this level indicating device, the measured value at the terminal of the contact strip is used to generate a corresponding level indication.
A device of this general type is known from German Published Unexamined Patent Application No. 2,435,841 and serves the purpose of reliably indicating the level of the liquid in the fuel tank even within the reserve range.
As a result of tolerances in the manufacture of the fuel tank and the fact that the weight of the liquid, depending on the fullness of the tank, can cause the bottom of the tank to bulge to a greater or lesser extent, the problem can occur that the distance between the top of the tank and the bottom of the tank is subject to variations. This has the consequence that, especially in the lower fullness range, a sufficiently high indication accuracy of the level in the liquid by a noncalibrated level indicator is no longer achievable. In order to overcome this problem, devices are known wherein the level indicator is composed of a protective tube which is deformable by joints and is fittable between the top of the tank and the bottom of the tank (German Published Unexamined Patent Application No. 3,339 325); or where the level indicator has spring means which ensure compensation for tolerance (German Published Unexamined Patent Application No. 3,307,288, German Patent No. 2,835,744).
In a dip tube sensor according to the general type, which as a rule, because of the structural conditions of the tank, is installed so that its dip tube forms an acute angle with respect to a perpendicular drop to the bottom of the tank, a problem can arise as a result of tolerances in the manufacture of the tank, especially in the flanging area of the sensor. Tolerances in the flanging area cause the installed position of the dip tube sensor to differ so that, primarily in the lower reading range, considerable measurement errors occur since the end of the dip tube is located at a greater or lesser distance from the bottom of the tank.
An object of the present invention is to provide a device for electrical measurement of the fuel in a tank which is able, despite any tolerances in the tank, to achieve high accuracy when measuring the fullness of the tank.
This object and other objects of the present invention are provided in a device for electrically measuring the level of a fluid contained in a fuel tank of a motor vehicle, by providing a device having a dip tube sensor with a travel sensor having a telescoping rod and a spring for pretensioning the telescoping rod out of the dip tube against the bottom of the tank. The telescoping rod has a telescope plate having a contact bridge with at least two wiper contacts. At least one travel sensor wiper contact is conductively connected with the resistance strip, while at least one other travel sensor wiper contact is conductively connected with a second contact strip such that a second measured value at a terminal of the second contact strip is functionally related to a calibration value for the device.
By virtue of the fact that the installed position of the dip tube sensor with respect to the bottom is sensed, it is possible for any measurement errors caused by tolerances to be eliminated by appropriate calibration. This correction is made automatically in certain preferred embodiments having a corresponding additional electrical design of the level-indicating device.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.